Progress in Bohai Offshore Heavy Oil Thermal Recovery

Abstract

Abstract Although there is abundant heavy oil resource in Bohai oilfield, only limited oil production is obtained by cold production technologies in past. The practical challenges of thermal production technologies such as steam injection for offshore heavy oil produciton include the difficulty to install the large conventional steam generator onto the production platform, and the large heat loss during steam injection in the long wellbore. In order to recover offshore heavy oil in Bohai Oilfield effectively in the limited production platform lifetime, a compact modular steam and gas generator was firstly introduced to generate steam, CO2 and N2 using diesel oil or natural gas as fuel, which could be injected into the offshore reservoir to enhance heavy oil production thermally. Usually, the temperature of generated steam could be regulated from 150 °C to 300 °C, and the operation pressure could be up to 20 MPa. The components including fuel tank, water treatment and air compressor could be easily resembled on the platform. At the same time, a compact modular steam generator was specially developed to for offshore steam injection process, in which N2 is usualy injected to make steam injection more effective to recover deep heavy oil reservoir. For the typical heavy oil reservoirs in Bohai Oilfield, the injection and production parameters such as steam injection volume and ratio of gas to water (GWR in short) are optimized for cyclic steam and flue gas stimulation (CSGS in short) and cyclic steam and N2 stimulation (CSNS in short) based on experiment and numerical simulation. Then, the engineering aspects such as corrosion prevention, isolation tubing and wellhead were provided for offshore operation. Since 2009, there are more than 20 wells in stimulated by CSGS, and 2 wells in stimulated by CSNS. In this paper, sheme optimization, engineering design and field test of CSGS and CSNS in Bohai Oilfield are introduced in detail. The result of field test shows that both the modular steam and flue gas generator and steam generator are feasible to operate on offshore platform and practicial to enhance offshore heavy oil production.